Controlling plating electrolyte concentration on an electrochemical plating apparatus

ABSTRACT

Methods and electroplating systems for controlling plating electrolyte concentration on an electrochemical plating apparatus for substrates are disclosed. A method involves: (a) providing an electroplating solution to an electroplating system; (b) electroplating the metal onto the substrate while the substrate is held in a cathode chamber of an electroplating cell of electroplating system; (c) supplying the make-up solution to the electroplating system via a make-up solution inlet; and (d) supplying the secondary electroplating solution to the electroplating system via a secondary electroplating solution inlet. The secondary electroplating solution includes some or all components of the electroplating solution. At least one component of the secondary electroplating solution has a concentration that significantly deviates from its target concentration.

INCORPORATION BY REFERENCE

An Application Data Sheet is filed concurrently with this specificationas part of the present application. Each application that the presentapplication claims benefit of or priority to as identified in theconcurrently filed Application Data Sheet is incorporated by referenceherein in their entireties and for all purposes.

TECHNICAL FIELD

The present disclosure relates to the control of electroplating solutionconcentration, and in particular to such control as conducted on anelectrochemical plating apparatus for semiconductor substrates.

BACKGROUND

Electrochemical deposition process is widely used in the semiconductorindustry for metallization of integrated circuit manufacturing. One suchapplication is copper (Cu) electrochemical deposition, which may involvedepositing of Cu lines into the trenches and/or vias that are pre-formedin dielectric layers. In this process, a thin adherent metaldiffusion-barrier film is pre-deposited onto the surface by utilizingphysical vapor deposition (PVD) or chemical vapor deposition (CVD). Acopper thin seed layer will then be deposited on top of the barrierlayer, typically by a PVD deposition process. The features (vias andtrenches) are then filled electrochemically with Cu through anelectrochemical deposition process, during which the copper cation isreduced electrochemically to copper metal.

SUMMARY

In an electrochemical plating apparatus that has isolated anolyte andcatholyte portions, the concentration of catholyte components (e.g.,acid, anions, cations, additives, etc.) may be controlled by adding asecondary electroplating solution (also sometimes called a secondaryelectrolyte) into the catholyte. The composition of the secondaryelectroplating solution compared to a primary electroplating solutiongenerally depends on chemical and/or physical reactions occurring duringelectroplating processes, but may be also designed to bring thecatholyte concentration to a target concentration with only a smallamount of dosing when compared to, e.g., the electroplating solutionreservoir volume. The dosing and/or addition of the secondaryelectroplating solution to the electroplating solution, in certainembodiments, may be need-based or time-based, depending on theapplication. In other words, while the secondary electroplating solutionis available, it might be used sparingly, if at all. For example, itmight only be used during the initial part of an electroplating run,during which the primary electroplating solution changes concentrationabruptly and significantly. Thereafter many substrates may beelectroplated in succession without using additional secondaryelectroplating solution.

Certain embodiments herein relate to methods for controlling theelectroplating solution concentration, and in particular to such controlas conducted on an electrochemical plating apparatus for semiconductorsubstrates. In one aspect of the embodiments herein, a method isprovided for electroplating metal onto a substrate during fabrication ofa device. The method may involve (a) providing an electroplatingsolution to an electroplating system comprising: (i) an electroplatingcell comprising an anode chamber and a cathode chamber and configured tohold the substrate in the cathode chamber while electroplating the metalonto the substrate, (ii) an electroplating solution reservoir configuredto hold a portion of the electroplating solution while electroplatingthe metal onto the substrate, (iii) a recirculation system fordelivering the electroplating solution between the electroplating celland the electroplating solution reservoir, (iv) a make-up solution inletfor providing make-up solution to the electroplating system, and (v) asecondary electroplating solution inlet for providing a secondaryelectroplating solution to the electroplating system, wherein theelectroplating solution includes multiple components for electroplatingthe metal onto the substrate; (b) electroplating the metal onto thesubstrate while the substrate is held in the cathode chamber; (c)supplying the make-up solution to the electroplating system via themake-up solution inlet, wherein the make-up solution includes some orall of the multiple components, each at a target concentration forelectroplating the metal onto the substrate, wherein supplying themake-up solution to the electroplating system changes the electroplatingsolution's composition so that at least one of the multiple componentsin the electroplating solution moves closer to its target concentration;and (d) supplying the secondary electroplating solution to theelectroplating system via the secondary electroplating solution inlet,wherein the secondary electroplating solution includes some or all ofthe multiple components, and wherein at least one component of thesecondary electroplating solution has a concentration that significantlydeviates from its target concentration.

The methods may involve repeating operations (b)-(d) to electroplate themetal onto a second substrate.

The methods may involve repeating operations (b)-(d) to electroplate themetal onto multiple additional substrates.

In some embodiments, the device may be an integrated circuit.

In some embodiments, the metal may be copper and/or cobalt.

In some embodiments, the multiple components of the electroplatingsolution may include metal ions and an acid.

In some embodiments, the multiple components of the electroplatingsolution may further include organic electroplating additives selectedfrom the group consisting of: an accelerator, a suppressor, a leveler,and any combination thereof.

In some embodiments, the multiple components of the electroplatingsolution may further include chloride ion and/or borate ion.

In some embodiments, the multiple components of the electroplatingsolution may further include copper ion, an acid, chloride ion, andorganic plating additives, and wherein the secondary electroplatingsolution contains acid at a target concentration for the acid and copperion at a copper ion secondary concentration that is significantly higherthan a target concentration for copper ion. The secondary electroplatingsolution may further include chloride ion at a target concentration forthe chloride ion, and/or wherein the secondary electroplating solutioncontains organic plating additives at a target concentration for theorganic plating additives. The copper ion secondary concentration may bebetween about 5 and 50 times greater than the target concentration forcopper ion. The secondary electroplating solution may further includechloride ion at a chloride ion secondary concentration that is higherthan a target concentration for the chloride ion.

In some embodiments, the multiple components of electroplating solutioninclude cobalt ion, an acid, borate ion, and organic plating additives,and wherein the secondary electroplating solution includes acid at atarget concentration for the acid, borate ion at a target concentrationfor borate ion, and cobalt ion at a cobalt ion secondary concentrationthat is significantly lower than a target concentration for cobalt ion.The target concentration for cobalt ion may be between about 5 and 50times greater than the cobalt ion secondary concentration.

In some embodiments, the multiple components of electroplating solutioninclude cobalt ion, an acid, borate ion, and organic plating additives,and wherein the secondary electroplating solution includes acid at atarget concentration for the acid, cobalt ion at a target concentrationfor cobalt ion, and borate ion at a borate ion secondary concentrationthat is significantly higher than a target concentration for borate ion.The borate ion secondary concentration is between about 1.2 and 2 timesgreater than the target concentration for borate ion.

In some embodiments, the multiple components of electroplating solutioninclude cobalt ion, an acid, borate ion, and organic plating additives,and wherein the secondary electroplating solution includes acid at atarget concentration for the acid, borate ion at a borate ion secondaryconcentration that is significantly higher than a target concentrationfor borate ion, and cobalt ion at a cobalt ion secondary concentrationthat is significantly lower than a target concentration for cobalt ion.

The methods may involve dosing a single component solution comprisingonly one of the multiple components for electroplating the metal ontothe substrate into the electroplating solution reservoir. The singlecomponent solution may be an aqueous chloride ion solution. Also, incertain embodiments, the single component solution may be an aqueousorganic electroplating additives solution.

In some embodiments, supplying the secondary electroplating solution tothe electroplating system includes supplying the secondaryelectroplating solution to the electroplating solution reservoir and/orthe cathode chamber of the electroplating cell.

In some embodiments, the electroplating cell further includes an iontransfer separator between the anode chamber and the cathode chamberconfigured to provide a path for ionic communication between theelectroplating solution in the anode chamber and the cathode chamber.The ion transfer separator may include a cation exchange membrane.

Certain embodiments herein relate to systems for electroplating metalonto a substrate during fabrication of a device. A system may involve(a) an electroplating cell comprising an anode chamber and a cathodechamber and configured to hold the substrate in the cathode chamberwhile electroplating the metal onto the substrate; (b) an electroplatingsolution reservoir configured to hold a portion of the electroplatingsolution while electroplating the metal onto the substrate; (c) arecirculation system for delivering the electroplating solution betweenthe electroplating cell and the electroplating solution reservoir; (d)an make up solution inlet for providing make up solution to theelectroplating system; (e) a secondary electroplating solution inlet forproviding a secondary electroplating solution to the electroplatingsystem; and (f) a controller configured to execute instructions for: (i)providing an electroplating solution to the electroplating system,wherein the electroplating solution includes multiple components forelectroplating the metal onto the substrate, (ii) electroplating themetal onto the substrate while the substrate is held in the cathodechamber, (iii) supplying the make up solution to the electroplatingsystem via the make up solution inlet, wherein the make up solutionincludes some or all of multiple components, each at a targetconcentration for electroplating the metal onto the substrate, whereinsupplying the make up solution to the electroplating system changes theelectroplating solution's composition so that at least one of themultiple components in the electroplating solution moves closer to itstarget concentration; and (iv) supplying the secondary electroplatingsolution to the electroplating system via the secondary electroplatingsolution inlet, wherein the secondary electroplating solution includessome or all of multiple components, and wherein at least one componentof the secondary electroplating solution has a concentration thatsignificantly deviates from its target concentration.

In some embodiments, the electroplating cell further includes an iontransfer separator between the anode chamber and the cathode chamberconfigured to provide a path for ionic communication between theelectroplating solution in the anode chamber and the cathode chamber.The ion transfer separator may include a cation exchange membrane. Incertain embodiments, the electroplating cell further may include one ormore auxiliary electrode chambers. The one or more one or more auxiliaryelectrode chambers may be one or more cathode chambers.

In some embodiments, the controller is further configured to executeinstructions for causing any one or more of the method operationsrecited above.

In one aspect of the embodiments herein, a method is provided forplating metal onto a substrate during fabrication of a device. Themethod may involve, (a) providing a plating solution to a platingsystem, the plating solution for plating the metal onto the substrateand including multiple components having target concentrations; (b)plating the metal onto the substrate; and (c) supplying a secondaryplating solution to the plating system wherein the secondary platingsolution includes some or all of the multiple components, and wherein atleast one component of the secondary plating solution has aconcentration that significantly deviates from its target concentration.

These and other features will be described below with reference to theassociated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments will now be described in conjunction with thedrawings, in which:

FIG. 1 is a schematic diagram of an exemplary plating electrolyte, orelectroplating solution, recirculation and/or dosing system.

FIG. 2 illustrates an electroplating bath-side vs. metal ion partitioneffect, e.g., showing the movement of metal ions selectively through asemi-permeable membrane.

FIGS. 3A-3D show various graphs illustrating electroplating bathconcentration drift as a result of electroplating conducted inaccordance with one or more embodiments disclosed herein.

FIG. 4 illustrates a relatively low plating current efficiency situationof that shown in FIG. 2.

FIGS. 5A-5C show various graphs illustrating electroplating bathconcentration trends without the introduction of a supplemental, orsecondary, electroplating solution to the system for that shown in FIG.4.

FIGS. 6A-6C show various graphs illustrating electroplating bathconcentration trends with acid dosing, e.g., to replenish acid, andde-ionized (DI) water dosing to control cobalt ion concentration [Co²⁺]for that shown in FIG. 4.

FIG. 7 shows a configuration of the electroplating system shown in FIG.1 with the introduction of a secondary electrolyte, or electroplatingsolution, for copper (Cu) plating.

FIGS. 8A-8B show various graphs illustrating bath concentration resultswith secondary make-up solution (MS) dosing for copper (Cu) platingelectrolyte.

FIG. 9 shows a configuration of the electroplating system shown in FIG.1 with the introduction of a secondary electrolyte, or electroplatingsolution, for cobalt (Co) plating.

FIGS. 10A-10C show various graphs illustrating expected bath performancewith secondary electrolyte dosing for cobalt (Co) plating.

FIG. 11A shows a configuration of the electroplating system shown inFIG. 1 with the introduction of a secondary electrolyte, orelectroplating solution, into the cathode side of the electroplatingcell. FIG. 11B shows a graph of auxiliary current as a function ofcation concentration in electroplating solution.

FIG. 12 shows a configuration of the electroplating system shown in FIG.1 with the introduction of a secondary electrolyte, or electroplatingsolution, into the anode side of the electroplating cell.

FIG. 13A-13E show various graphs illustrating primary electroplatingsolution and anolyte concentration trends for dosing cobalt (Co²⁺) tothe anode chamber of the electroplating cell.

FIG. 14 shows a schematic of a top view of an example electrodepositionapparatus.

FIG. 15 shows a schematic of a top view of an alternative exampleelectrodeposition apparatus.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the presented embodiments.The disclosed embodiments may be practiced without some or all of thesespecific details. In other instances, well-known process operations havenot been described in detail to not unnecessarily obscure the disclosedembodiments. While the disclosed embodiments will be described inconjunction with the specific embodiments, it will be understood that itis not intended to limit the disclosed embodiments.

Introduction and Context

Control of the composition and concentration of the electroplatingsolution used in an electroplating system may be important to theperformance of the electrochemical deposition process. Typically, thereare multiple components in a given electroplating solution. For example,the composition of electrolyte used for the deposition of copper on awafer may vary, but may include sulfuric acid, copper salt (e.g.,CuSO₄), chloride ion, and a mixture of organic additives. Thecomposition of electroplating solution is selected to optimize the rateand uniformity of electroplating inside features of the wafer, or in thefield of the wafer, e.g., an area without features formed on or in thewafer. During the plating process, copper salt serves as the source ofcopper cation, and also provides conductivity to the electroplatingsolution; further, in certain embodiments, sulfuric acid enhanceselectroplating solution conductivity by providing hydrogen ions ascharge carriers. Also, organic additives, generally known in the art asaccelerators, suppressors, or levelers, are capable of selectivelyenhancing or suppressing rate of copper (Cu) deposition on differentsurfaces and wafer features. Chloride (Cl) ion is useful for modulatingthe effect of organic additives, and may be added to the electroplatingbath for the purpose. In some implementations, another halide (e.g.,bromide or iodide) is used in place of or in addition to chloride.

Generally, separation of anodic and cathodic regions of anelectroplating cell by a semi-permeable membrane may be desirable sincechemical processes occurring at the anode and at the cathode duringelectroplating may not necessarily be compatible. For example, duringoperation, insoluble particles may form on the anode. Protection of thewafer from such insoluble particles is often desirable to avoidinterference of such particles with subsequent metal depositionprocesses conducted on the wafer. Also, the restriction of organicadditives to the cathodic portion of the plating cell may also bedesirable to prevent such additives from contacting and/or reacting withthe anode. For instance, a suitable separating membrane would allow forthe flow of ions, and hence, current, between the anodic and cathodicregion of the plating cell, but will still restrict unwanted particlesand/or organic additives from permeating through the separatingmembrane. Thus, usage of the separating membrane duringelectrodeposition will create different chemical environments in thecathodic and anodic regions of a plating cell equipped with theseparating membrane. Electrolyte contained in the anodic region of theplating cell may be referred to as the “anolyte.” Likewise, electrolytecontained in the cathodic region of the plating cell may be referred toas the “catholyte.”

An electroplating apparatus having a membrane to separate the anodicregion from the cathodic region is described in further detail in U.S.Pat. No. 6,527,920 entitled “Copper Electroplating Apparatus” to Mayeret al. and is incorporated in its entirety herein by reference. Asdiscussed above, such a separating membrane allows current to flowbetween the anodic region and the cathodic region, but may be furtherconfigured to selectively restrict current flow depending on the type ofion. That is, the membrane separating the catholyte and anolyte maydemonstrate selectivity for different types of ions. For example, for aCu plating application, the separating membrane may allow passage ofhydrogen ions (H⁺) at a faster rate than the passage rate of copperions, e.g., Cu²⁺ and/or Cu⁺. Depending on the selectivity of themembrane, the mobility of particular types of ions or current moregenerally may be predominantly carried by hydrogen ions, until a certainmolar ratio between, for example, Cu²⁺ and H⁺ concentrations isachieved. After this ratio is achieved, copper ions and hydrogen ionsmay begin to carry current across the membrane proportionally so thatCu²⁺ and acid concentration in the anodic portion of the electrochemicalcell stabilize. Therefore, until a certain molar ratio between copperions and hydrogen ions is achieved, the anolyte may be continuouslydepleted of its acidic component, since hydrogen ions are the maincurrent carriers under these conditions. Concurrent with the depletionof the acidic component of the anolyte, the concentration of copper saltis increased, especially when a copper-containing anode is used. Theabove effect, e.g., depletion of acid from the anolyte with acommensurate increase in copper salt, may be referred to in the art asan “acid/metal ion partition effect” taking place inside the anodechamber, or “anode chamber depletion effect,” since acid is depleted inthe anode over a period of time.

The acid/metal partition processes described above may alsoinadvertently result in several undesirable side effects on the platingsystem. Several such side effects are described in U.S. Pat. No.8,128,791 (herein the '791 patent) entitled “Control of ElectrolyteComposition in a Copper Electroplating Apparatus” to Buckalew et al.,incorporated by reference in its entirety herein. Undesirable sideeffects include potential crystallization, or precipitation, of excesssalt from the electroplating solution onto the anode surface inside theanode chamber. Also, water may seep across the membrane due to theelectro-osmotic effect by creating pressure gradient between the anodicportion and cathodic portion of the apparatus, which may ultimately leadto membrane damage and failure. U.S. Pat. No. 8,128,791 describes waysof controlling the anodic electrolyte composition by frequentlyreplenishing the anode chamber with plating electrolyte. Such a processmay be referred to in the art as “bleed and feed.” Alternative to bleedand feed, diluted electrolyte may be added into the anode chamber of theplating cell.

The acid/metal ion partition effect, described above, may also createundesirable electroplating solution concentration fluctuation on thecathodic side of an electroplating cell, which, in turn, may impactelectroplating process performance. A few examples are described below.

To understand the above discussed phenomenon, a typical electrolytemanagement system is illustrated in FIG. 1. As shown, there are a fewmajor segments, e.g., an anode solution loop 132 and/or a cathodesolution loop 118, in an electrolyte management system 100. Typically,there is a central bath 102 that provides electroplating solution to aplating cell 148 and a main cathode chamber 122. The central bath 102includes a solution recirculation loop (not shown in FIG. 1).Additionally, in certain embodiments or configurations, the central bathmay also have a temperature control, and a dosing system such as thatfor additive dosing, deionized water (DI) dosing, and dosing of otheractive bath components. Further, in some embodiments, the central bath102 may be equipped with a draining or overflow line 146 leading awayfrom the central bath 102 to remove unwanted electroplating solutionwhen appropriate. Moreover, in a plating apparatus, such as the platingcell 148, with separate anodic and cathodic portions, the anodicportion, such as main anode chamber 126, may have a dedicatedrecirculation loop 132, and dosing line (not shown in FIG. 1), andoverflow and/or drain line (not shown in FIG. 1). In such aconfiguration, the main cathode chamber 122 may be configured to receiveplating electrolyte from the central bath 102, circulate the electrolytetoward the plating cell 148 by a feed line 112 and direct overflow backto the central plating bath 102 by cell and/or overflow drain line 142.One skilled in the art will appreciate that the configuration shown inFIG. 1 is exemplary and many other suitable configurations may existwithout departing from the scope of the disclosure. Further, certainvariations and/or configurations of system 100 shown in FIGS. 1, 7, 9,11A and 12 are intended to be representative schematics only and not tobe interpreted as literal layouts or configurations of system 100.

The electrolyte management system 100 shown in FIG. 1 will be used todescribe variants of the system 100 in relation to supplying asecondary, or supplemental, electrolyte to various system 100 componentsto regulate undesirable electroplating solution concentrationfluctuation on either the cathodic or anodic sides of the plating cell148. Such variants are shown in FIGS. 7, 9, 11A and 12 and described infurther detail below. Generally, system 100 shown in FIG. 1 includes thecathode solution loop 118 and the anode solution loop 132, which, incertain embodiments, may be in fluid communication with one anotherthrough the bath 102 contained in an electroplating solution reservoir150. During normal operation of system 100, incoming platingelectrolyte, sometimes called make-up solution, having a definedconcentration of metal ion in solution with acid, is provided to system100 via line 108. Various regulation points 110, such as valves,pressure, and/or flow controllers may be installed on line 108, and/orother lines similar thereto, to regulate fluid flow through the lineupon which the regulation point 110 is installed. Similarly, mixingpoint 112 may receive fluid flow from an incoming line 108. Mixingpoints 112 may likewise be installed as needed throughout system 100 toregulate delivery and quantity of fluid flowing through lines 108, etc.

Thus, incoming plating electrolyte may flow through regulation point 110to enter bath 102 to accumulate in the reservoir 150 intended to holdbath 102. In certain embodiments, organic additives are flowed into bath102 via line 104. Similarly, de-ionized (DI) water may be flowed intobath 102 via line 106 to regulation concentration levels of the variouscomponents, or ingredients, of bath 102. Operation of system 100 mayinvolve the pumping of bath 102 fluid through line 116 toward thecathode side 122 of the plating cell 148 for accumulation therein. Incertain embodiments, a cathode 128 may be at least partially submergedin the cathode side 122 and electrically connected to an anode 130,which may be similarly submerged in the anode side 126 to complete anelectric circuit 134. Further, electrical current (or more precisely theelectrons carrying the current) is generally in the direction 136, e.g.,from the negatively charged anode 130 to the positively charged cathode128. The electric current drives reaction of metal ions, e.g., copperions, Cu²⁺, in solution with acid in the cathode side, or compartment,122, allowing for electroplating of such copper metal on a wafer 200, asshown in FIG. 2, positioned in the cathode side 122 of the plating cell148.

Solution from the cathode side 122 may be pumped through a celloverflow, or drain, line 138 back to bath 102 as needed. Similarly,solution from the anode side 126 may be pumped through an anode drainline 142 also to the bath 102 as needed. Overflow from bath 102 may beintermittently be pumped out of system 100 through a bath overflow, ordrain, line 146, which may be referred to more generally as a bathdosing and overflow control loop 144. In certain embodiments, the bathdosing and overflow control loop may include a recirculation pump (notshown), a dosing line (not shown), the bath overflow line 146, and atemperature control apparatus and/or mechanism (not shown). Togethersupplying make-up solution via line 108 and dumping electrolyte from thereservoir 150 holding primary electroplating solution, or bath, 102serves as the bleed and feed process.

A factor to consider during supply of plating electrolyte to thecathodic side 122 to conduct electroplating on a wafer contained thereinis the acid/metal ion partition effect, as described earlier. Thiseffect can be observed in a copper plating process and may apply toother similar plating system. As illustrated in FIG. 2, on the anode, Cuions, e.g., shown as metal ions, or Me⁺, are de-plated into the anodicsolution due to the passing of direct electric current through theoxidation reaction of Cu→Cu²⁺+2e. On the cathode side 122, the Cu²⁺ ionsare extracted from the solution through the reaction of Cu²⁺+2e→Cu.Analogously, across membrane 124 on the anode side 126, due to acidcarrying a large portion of the plating current, the anodic electrolyte,which had become metal ion rich, slowly depletes acid or H⁺ ions, overtime. On the cathode side 122, since metal ions (e.g., cupric ions forCu plating) are removed from solution upon electroplating orelectrodeposition upon wafer 200 contained therein, while the solutionflowing across the separation membrane (from anode chamber to cathodechamber) is acid rich. As mentioned, ionic transfer through the membranefavors hydrogen ions over copper ions. Thus, copper ion concentration inthe cathode side 122 would drop over time, while acid concentrationtherein would increase, as illustrated in FIG. 3B, e.g., showing aninitial spike in acid concentration followed by eventual taperingthereof as concentration levels approach a steady-state condition. Asdescribed elsewhere, the acid metal ion partition effect may be obviatedby adopting a high electrolyte replenish rate to the anodic side 126and/or on the bath 102, which in fluid communication with the cathodicside 122 in many configurations. But high replenish rates canunnecessarily waste electroplating solution and increase the operationcost of the electroplating apparatus.

The acid/metal ion partition effect may have a substantial impact onelectroplating solutions having a relatively low metal ion concentration(e.g., about 5 g/l or lower). In such solutions, a concentration changeof as little as a few tenths of a gram per liter can greatly impact theoverall concentration of the metal ion in the solution and hence overallelectroplating performance. For example, if the target copper ionconcentration is about 2 g/l and the concentration drift depletes about0.6 g/l of copper from the catholyte, the concentration has now droppedby 30% and the plating performance may therefore experience asignificant negative impact.

Other variations observed of plating with metals other than copper areshown in Figures through 6A-6D. More particularly, cobalt (Co) may beselected to be used as the metal for such plating processes. As in acopper plating electrolyte, the cobalt plating electrolyte may beconfigured to include cobalt salts, sulfuric acid, organic additives,and boric acid as a buffer solution.

In this plating process, as in previous Cu plating example, metal ionsare stripped from the anode through the following reaction: Me-e→Me⁺.Simultaneously, at the cathode surface, due to lower than 100% platingcurrent-efficiency for metal plating (current efficiency is defined hereas the metal plating (Me⁺+e→Me) current as a percentage of the totalcurrent delivered to the anode), the two reduction reactions happen atthe same time: Co²⁺+2e→Co and 2H⁺+2e→H₂. The amount of current consumedby each reaction varies between plating process settings. Over a longterm, the net effects of this plating process on the plating bathelectrolyte are: (1) metal ion concentration increase since more isreleased from anode than consumed at cathode; (2) acid concentrationdrop since acid is only consumed on the cathode side without beingsupplied from the anode; (3) boric acid (H₃BO₃) concentration does notchange since boric acid is not actively involved in the reaction. Thisis illustrated in FIG. 5. Note that if the acid metal ion partitioneffect happened in the anodic side could further shift the metal ion andacid concentration if the amount of charge carried by acid through themembrane is significant. But in some applications, due to the much lowerconcentration of acid as compared to the metal ion concentration, thepartition effect becomes negligible. For simplicity of discussion here,the partition effect on cathodic electrolyte concentration for this kindof plating process was not included.

With the net consumption of acid from the plating electrolyte, aciddosing to the plating bath may be implemented in the above discussedsystem, e.g., the electrolyte management system 100. For processperformance considerations, Co ion concentration would also needs to becontrolled, by adding de-ionized (DI) water to the plating electrolyte.As a result of both acid and DI dosing to the bath, boric acidconcentration would drop over time without any dosing mechanism. This isillustrated in FIG. 6. Since boric acid (any other component of similarfunction in other metal electroplating process) may be important for theCo plating process, the concentration of boric acid needs to beaddressed as well.

On a plating apparatus, it is sometimes desirable to have an auxiliarycathode, as disclosed in U.S. Pat. No. 8,308,931 entitled “Method andApparatus for Electroplating” to Reid et al., and U.S. Pat. No.8,475,644 entitled “Method and Apparatus for Electroplating” to Mayer etal. both incorporated herein by reference in their entireties.Implementing an auxiliary cathode, or auxiliary anode, in an electrolytemanagement system provide certain advantages. The auxiliary cathodes areusually contained in small isolated chambers to avoid contacting withthe main cathode (wafer substrate in a plating apparatus), and they areusually of smaller size as compared to the main cathode (wafersubstrate). It is sometimes desirable to have different concentrationfor the electrolyte in the auxiliary cathode chamber. For example, it issometimes preferred to have higher anion concentration (than in theplating electrolyte for main cathode) in the auxiliary cathode chamberso that higher current could be applied on the auxiliary cathode.

Definitions

The following terms are used intermittently throughout the instantdisclosure:

“Substrate”—In this application, the terms “semiconductor wafer,”“wafer,” “substrate,” “wafer substrate” and “partially fabricatedintegrated circuit” are used interchangeably. One of ordinary skill inthe art would understand that the term “partially fabricated integratedcircuit” can refer to a silicon wafer during any of many stages ofintegrated circuit fabrication thereon. A wafer or substrate used in thesemiconductor device industry typically has a diameter of 200 mm, or 300mm, or 450 mm. Further, the terms “electrolyte,” “electroplating bath,”“plating bath,” “bath,” “electroplating solution,” and “platingsolution” are used interchangeably. The following detailed descriptionassumes the embodiments are implemented on a wafer. However, theembodiments are not so limited. The work piece may be of various shapes,sizes, and materials. In addition to semiconductor wafers, other workpieces that may take advantage of the disclosed embodiments includevarious articles such as printed circuit boards, magnetic recordingmedia, magnetic recording sensors, mirrors, optical elements,micro-mechanical devices and the like.

“Metal”—a material (an element, compound, or alloy) that is, for thepurposes of this disclosure, desirable for plating onto a substrate orwafer. Examples include copper, cobalt, tin, silver, nickel, and alloysor combinations of any of these.

“Electroplating cell”—a cell, typically configured to house an anode anda cathode, positioned opposite to each other. Electroplating, whichtakes place on the cathode in an electroplating cell, refers to aprocess that uses electric current to reduce dissolved metal cations sothat they form a thin coherent metal coating on an electrode. In certainembodiments, an electroplating cell has two compartments, one forhousing the anode and the other for housing the cathode. In certainembodiments, an anode chamber and a cathode chamber are separated by asemi-permeable membrane that permits for the selective movement ofconcentrations of ionic species therethrough. The membrane may be an ionexchange membrane such as a cation exchange membrane. For someimplementations, versions of Nafion™ (e.g., Nafion 324) are suitable.

“Anode chamber”—a chamber within the electroplating cell designed tohouse an anode. The anode chamber may contain a support for holding ananode and/or providing one or more electronic connections to the anode.The anode chamber may be separate from the cathode chamber by asemi-permeable membrane. The electrolyte in the anode chamber issometimes referred to as anolyte.

“Cathode chamber”—a chamber within the electroplating cell designed tohouse a cathode. Often in the context of this disclosure, the cathode isa substrate such as a wafer such as a silicon wafer having multiplepartially fabricated semiconductor devices. The electrolyte in thecathode chamber is sometimes referred to as catholyte.

“Electroplating solution (or electroplating bath, plating electrolyte,or primary electrolyte)”—a liquid of dissociated metal ions, often insolution with a conductivity enhancing component such as an acid orbase. The dissolved cations and anions disperse uniformly through thesolvent. Electrically, such a solution is neutral. If an electricpotential is applied to such a solution, the cations of the solution aredrawn to the electrode that has an abundance of electrons, while theanions are drawn to the electrode that has a deficit of electrons.

“Make-up solution”—a type of electroplating solution that typicallycontains all or nearly all components of the primary electroplatingsolution. Make-up solution is provided to an electroplating solution tomaintain the concentration of solution components within desired ranges,chosen to maintain good electroplating performance. This approach isused because concentrations of components vary in the solution drift orvary with time due to any of a number of factors as described below.Make-up solution is often provided as the “feed” of a bleed and feedsystem. Often the concentrations of components in the make-up solutionare similar or identical to the target concentrations for thosecomponents. Some make-up solutions do not include organic platingadditives.

“Recirculation system”—provision of fluid substances back into a centralreservoir for subsequent re-use. A recirculation system may beconfigured to efficiently re-use electroplating solution and also tocontrol and/or maintain concentration levels of metal ions within thesolution as desired. A recirculation system may include pipes or otherfluidic conduits together with a pump or other mechanism for drivingrecirculation.

“Target concentration”—a concentration level of metal ions and/or othercomponents in the electroplating solution used to achieve desiredplating performance. In various embodiments, components of the make upsolution are provided at the target concentrations.

“Secondary electroplating solution (or secondary electrolyte)”—Anadditional electroplating solution, similar to the make-up solution, buthaving a concentration of metal ion or other component thatsubstantially deviates from its target concentration in theelectroplating solution. In certain embodiments, the secondaryelectroplating solution is applied to remedy undesirable concentrationdrift of one or more components in the electroplating solution.

Concentrations recited in g/l refer to the total mass of a component ingrams per one liter of solution. For example, a 10 g/l concentration ofcomponent A means that 10 grams of component A are present in a oneliter volume of the solution containing component A. When specifying aconcentration of an ion such as copper ion or cobalt ion in g/l, theconcentration value refers to the mass of the ion alone (not the salt orsalts from which the ion was produced) per unit volume of solution. Forexample, a concentration of 2 g/l of copper ion contains 2 g of copperion per liter of solution in which the copper ion is solubilized. Itdoes not refer to 2 grams of copper salt (e.g., copper sulfate) perliter of solution or otherwise refer to the mass of the anion. However,when referring to the concentration of an acid such as sulfuric acid,methane sulfonic acid, or boric acid, the concentration value refers themass of the entire acid (hydrogen and anion) per unit volume. Forexample, a solution having 10 g/l sulfuric acid contains 10 grams ofH₂SO₄ per liter of solution.

Electroplating Systems Using a Secondary Electrolyte

Included in this disclosure are a method and an apparatus allowingpractice of such a method, to control the plating electrolyteconcentration provided to a plating apparatus, primarily directed to thecathodic side of the apparatus. In certain embodiments, a similarapproach may be used to control the electrolyte concentration in theanodic portion of the plating apparatus, which could in turn impact theelectrolyte concentration on the cathodic side.

A method disclosed herein involves adding a secondary or supplemental,plating electrolyte to the plating apparatus, which may receive and usea plating electrolyte of a target concentration for plating onto themain cathode (wafer substrate).

The secondary electrolyte is often of a different composition from theprimary plating electrolyte or a target concentration thereof. Examplesof features of the secondary electrolyte include that:

(1) The secondary electrolyte contains most, or all, of the componentscontained by the primary electrolyte. In certain embodiments, thesecondary electrolyte lacks organic plating additives, while the primaryelectrolyte includes such additives. In various embodiments, thesecondary electrolyte includes all but one or all but two of thecomponents of the primary electrolyte. For example, in a copper-acidplating system, the secondary electrolyte may lack chloride ion and/ororganic plating additives, but otherwise has all the other remainingcomponents of the copper-acid primary electrolyte. In another example, acobalt-acid plating system may employ a secondary electrolyte that lackscobalt ions and/or organic plating additives, but otherwise has all theother remaining components of the cobalt-acid primary electrolyte.

(2) Most, but not all, the components of the secondary electrolyte mayhave the same, or substantially the same, concentration as in theprimary electrolyte, particularly the target concentrations of suchcomponents in the primary electrolyte. In some cases, these componentsof the secondary electrolyte have the same, or substantially the same,compositions as in a make up solution (MS). For example, in anacid-copper plating system, the secondary electrolyte may include acidand chloride ion at concentrations that are substantially the same asthose in the primary electrolyte. In another example, in an acid-cobaltplating system, the electrolyte may include acid and cobalt ion atconcentrations that are substantially the same as those in the primaryelectrolyte.

(3) At least one of the components in the secondary electrolyte has asignificantly different concentration than the primary electrolyte'starget concentration. In an acid-copper plating system for example, thetarget concentration of copper ion in the primary electrolyte may beabout 2 g/l, and the concentration of copper ion in the secondaryelectrolyte may be about 40 g/l. In an acid-cobalt plating system forexample, the target concentration of borate ion in the primaryelectrolyte may be about 33 g/l, while the concentration of borate ionin the secondary electrolyte may be about 45 g/l (e.g., the solubilitylimit of borate).

(4) The component(s) of the secondary electrolyte that is (are)significantly different in concentration are the same component(s) inthe primary electrolyte which would experience the most drift incomposition or concentration, given a normal processing without using asecondary electrolyte, e.g., copper ion and acid in FIGS. 3A-3D andborate ion in FIG. 6C. In some cases, particularly those involving asignificant acid/metal ion partition effect, a significant drift istransient (i.e., it occurs only temporarily and is not permanent). SeeFIGS. 3B-3D. For example, the drift may only be significant uponstarting operation after replacing much or all of the electrolytesolution. As an example, the transient drift may exist for a durationcorresponding to plating on about 300-1,000 wafers, or over the courseof approximately one day. In some implementations, it is only during thetransient period of significant drift that the secondary electrolyteneed be employed.

(5) Depending on the direction of the drift in a component'sconcentration in the primary electrolyte during usage, the concentrationof the component in the secondary electrolyte is significantly higher orlower in concentration. For example, given the acid concentration'spositive “drift” in the catholyte shown in FIG. 3D, a secondaryelectrolyte may include a significantly reduced concentration of acid.The concept of “drift,” as understood in the art and referred to hereinmay be considered a perturbation from a target concentration value. Forexample, a drift may be a perturbation of more than about 2-3% from aspecified target value. In another example, given the copper ionconcentration's negative drift in the catholyte shown in FIG. 3C, asecondary electrolyte may include a significantly increasedconcentration of copper ion. In still another example, given the borateconcentration's negative drift in the catholyte shown in FIG. 6C, asecondary electrolyte may include a significantly increasedconcentration of borate ion.

(6) The volume usage of the secondary electrolyte may be relativelyinsignificant when compared to the volume of the central plating bath(primary electroplating solution) or the reservoir holding that bath,e.g., reservoir 150 shown in FIGS. 1, 7, 9, 11A, and 12. This has thebenefit reducing reliance on consumable ingredients and thus may allowfor designs or configurations that do not increase, or not significantlyincrease, the footprint of the plating apparatus. In an example, theamount of secondary electrolyte used in one day of continuous platingoperation (e.g., to plate about 1,000 wafers) is no more than 5% of thevolume of the electroplating solution reservoir.

(7) Use of the secondary electrolyte may significantly reduce therequired bleed and feed rate to maintain the primary electrolyte incontrol specification. The amount of reduction in the bleed and feedrate depends on the particular plating system application. In aninstance where make-up solution has a cupric ion concentration of about2 g/l, the bleed and feed rate required to control copper ionconcentration to within 5% to target may be greater than about 150%. Forthe same applications but with the use of a secondary electroplatingsolution as described herein, the bleed and feed rate may be reduced toonly 15%, and yet have similar, or even better, control over copperconcentration in the solution. A bleed and feed rate refers to thefraction of fluid volume in the electroplating solution reservoir thatis replaced (bled off or fed in) during one day of continuouselectroplating. For example, if the reservoir holds 150 L ofelectroplating solution, a bleed and feed rate of 15% requiresreplacement of 22.5 L of electroplating solution during a day ofcontinuous electroplating.

(8) Additions of the secondary electrolyte to the primary electrolyte,or to the auxiliary cathode chamber, are based on primary electrolytecomposition, and may not always be needed. For example, secondaryelectrolyte additions may not always be needed outside of transientconcentration deviations due to results of the acid/metal ion partitioneffect.

(9) In certain embodiments, the secondary electrolyte may be supplied tothe plating apparatus through a small container attached to the platingapparatus. Moreover, in certain embodiments, supplying the secondaryelectrolyte is done through a bulk facility supply (e.g., a source thatis available to multiple tools in a fabrication facility, and may beplumbed through the facility).

(10) In some embodiments, the secondary electrolyte is introduced to themain electroplating solution reservoir. Also, in certain embodiments,the secondary electrolyte is introduced to the cathode chamber of aplating cell and/or to an auxiliary cathode chamber of the plating cell.In some applications, the secondary electrolyte is introduced to theanode chamber of a plating cell. This latter application may helpmaintain the cathode side electrolyte concentration to specification.Various orientations and/or configurations of the supply of secondaryelectrolyte to various components of the electrolyte management system100, shown in FIG. 1, are shown in FIGS. 7, 9, 11A, and 12 and will bedescribed in further detail below.

When specifying concentration values, “substantially the same” meanswithin about +/−5% from a specified target value. For example, aconcentration that is substantially the same as 2 g/l may be within arange of about 1.9 to 2.1 g/l. Unless otherwise noted when specifyingconcentration values, “significantly deviate from,” “is significantlydifferent than,” and the like mean that the more concentrated componenthas a concentration that is between about 1.3 times and 50 times theconcentration of the less concentrated component. In some cases, theconcentration difference of a component in (a) a secondaryelectroplating solution and (b) a primary electroplating solution or amake up solution, is between about 5 to 50 times. For example, theconcentration of component A is about 5 to 50 times greater in thesecondary electroplating solution than in the primary electroplatingsolution, or vice versa. In another example, the concentration ofcomponent A is about 5 to 20 times greater in the secondaryelectroplating solution than in the primary electroplating solution, orvice versa. In yet another example, the concentration of component A isabout 15 to 30 times greater in the secondary electroplating solutionthan in the primary electroplating solution, or vice versa.

As described previously, component concentration drift in a platingelectrolyte may be common. This is especially true for a platingapparatus with separate anodic and cathodic portions, but may not benecessarily tied to that kind of design. To maintain both catholyte andanolyte concentration to acceptable level to ensure acceptableelectrochemical plating performance, a general approach in controllingthe electrolyte concentration is to adopt a high electrolyte replenish(e.g., “bleed and feed”) rate. However, doing so may increaseoperational costs of running plating processes significantly, andsometimes make the plating process prohibitively expensive. In addition,in some cases, application and/or usage of a high bleed and feed ratealone may not adequately address the electrochemical plating performancerelated problems. A second approach that could be used is to haveseparate dosing for each and every component in the electrolyte.However, doing so could make the dosing algorithm extremely complicated.Additionally, dosing of every component to the plating electrolyte wouldgenerate a diluting effect to all other components in the platingelectrolyte. Thus, the plating apparatus could end up being indosing/calculating status all the time. Accordingly, this approach isgenerally avoided.

By adopting a “complementary” secondary electroplating solution, thereplenish rate could be significantly reduced, while the concentrationdrift in the primary plating electrolyte could be significantly reduced.By designing the secondary electrolyte properly, the usage of secondaryelectrolyte could be minimized so that adopting secondary electrolytewould not contribute toward substantial additional costs to setting upand running the plating apparatus.

Example (1)—Copper Electroplating

Cu-like plating process, where Cu plating current efficiency is high(close to 100%), and where there is a strong acid metal ion partitioneffect in the anodic electrolyte. As described in the previous sectionsand shown in FIG. 2 and FIGS. 3A through 3D, a potential issue with thisplating process is acid drifting low and Cu concentration drifting highin the anodic portion, and acid drifting high and Cu drifting low in thecathodic portion. In certain embodiments, the copper electroplatingsolution includes copper sulfate, sulfuric acid, chloride ions, organicadditives, and deionized (DI) water as needed. Typical concentrationranges for such components include about 1-25 g/l Cu ion, about 10-175g/l acid, about 40-100 ppm chloride ion, and about 20-400 ppm additives.In certain embodiments, a low concentration copper electroplatingsolution is used; i.e., a solution having about 10 g/l Cu ion or lessand about 5-50 g/l acid. In certain embodiments, a low concentrationcopper electroplating solution contains about 4-10 g/l Cu ions and about5-20 g/l acid.

FIG. 7 illustrates a plating electrolyte concentration control schemewith secondary electrolyte. Like reference numerals refer to likeelements, thus a redundant description of the same will be omitted.Building upon that described in detail for system 100 shown in FIG. 1,system 700 further may be configured to include delivery of incomingplating electrolyte, which now may include metal ions of a first definedconcentration level, denoted by [Me⁺]_(a), acid, e.g., ionized and/orhydrogen ions shown by [H⁺]_(a), and chloride ions, shown by [Cl⁻]_(a).Unlike system 100, system 700 shown by FIG. 7 has an additional line 704feeding, or otherwise supplying, secondary electrolyte, e.g., tocompensate for undesirable plating solution concentration fluctuation onthe cathodic side 122, and/or the anodic side 126. The secondaryelectrolyte may include metal ions of a second defined concentrationlevel, different from the first defined concentration level, denoted by[Me⁺]_(b), and may otherwise have the original concentration levels ofacid as the incoming plating electrolyte, e.g., hydrogen ions shown by[H⁺]_(a), and chloride ions, shown by [Cl⁻]_(a). In the depictedembodiment, secondary electrolyte is supplied to bath 102 contained inreservoir 150.

In one implementation, the secondary electrolyte is designed to havesignificantly higher [Me+] (e.g., Cu²⁺) than in the bath, while othercomponents (e.g., acid, Cl⁻) remain of the same concentration. Theplating electrolyte concentration could be maintained by dosingsecondary electrolyte when [Me+] in cathodic side drifts low, doing sowill bring [Me+] up to target without impacting other components; dosingDI when [H⁺] in the cathodic portion drift high, and add secondaryelectrolyte to maintain the [Me+] concentration, if needed. As anexample, the make-up solution includes about 1-5 g/l copper ion, about5-20 g/l acid, and about 40-80 ppm chloride ion, while the secondaryelectroplating solution includes about 30-80 g/l copper ion, about 5-20g/l acid, and about 40-80 ppm chloride ion. Either or both of the makeup solution and the secondary electroplating solution optionally includeone or more organic plating additives.

In another implementation, the secondary electrolyte could be designedto have significantly higher [Me+] concentration, yet slightly higherconcentration in [Cl⁻], and slightly lower concentration in [W]. Forexample, assuming a target electroplating solution of about 1-25 g/l Cuion, about 10-175 g/l acid, about 40-100 ppm chloride ion, and about20-400 ppm additives, the secondary electroplating solution may have aconcentration in the range of about 20-70 g/l copper ion, about 8-10 g/lacid, and about 50-100 ppm chloride ion.

In yet another embodiment, the secondary electrolyte could be designedto be metal sulfate (CuSO₄) solid powder. In that case, a very smallamount of powder addition to the bath would bring anion concentrationback to target, yet it will not cause plating bath volume change so itwill not impact the concentration levels of the other components.

FIGS. 8A and 8B show typical [Cu²⁺] and acid concentration trends,respectively, in a plating electrolyte on a plating apparatus that hasadopted secondary electrolyte. This shows significant improvement in[Cu²⁺] and acid concentration drift.

Example (2)—Cobalt Electroplating

Plating processes for electroplating cobalt onto a wafer, whereacid/metal ion partition effect in the anodic side is not significant,and where metal plating current efficiency is <100%, are shown in detailby system 900 in FIG. 9. Over long term of plating, Co²⁺ concentrationmay drift high, while acid (H₂SO₄) concentration drift low over time,with boric acid concentration remaining relatively stable. See FIGS.5A-5C. As illustrated in FIG. 5A and FIG. 6C, depending on the controlalgorithm used on the plating apparatus, with acid dosing enabled, theend results could be either Co²⁺ concentration getting too high (if Co²⁺is not controlled) over time, or H₃BO₃ concentration drifting low (ifCo²⁺ concentration is controlled with DI addition). FIG. 9 illustrates aplating electrolyte control schematic on a Co plating apparatus. Incertain embodiments, the cobalt electroplating solution includes cobaltsulfate, sulfuric acid, boric acid, organic additives, and deionizedwater as needed. Typical concentration ranges for such componentsinclude about 2-40 (Co²⁺)g/l, about 10-40 g (H₃BO₃)/l (boric acid),about 0.01-0.1 g (H₂SO₄)/l (e.g., sulfuric acid), and about 20-400 ppmorganic plating additives.

Similar to that introduced for system 700 shown by FIG. 7, system 900,which may be used for plating cobalt, may include the delivery of asecondary electrolyte via line 904 to bath 102. Like reference numeralsrefer to like elements, thus a redundant description of the same will beomitted. In system 900, both the incoming plating electrolyte and thesecondary electrolyte may include boric acid, e.g., H₃BO₃, as aconstituent in solution, sometimes used in place of Cl⁻ in cobaltplating solutions. In the depicted embodiment, the make-up solutionprovided via line 108 includes metal ion (e.g., cobalt ion), acid (e.g.,sulfuric acid), and boric acid. In this embodiment, the secondaryelectrolyte is supplied to bath 102 contained in reservoir 150.

The secondary electrolyte is designed to have significantly lower Co²⁺concentration (as low as 0 g/l) yet have the same concentration of H₃BO₃and acid. For example, the secondary electroplating solution may containbetween 0-1 g (Co²⁺)/l (e.g., cobalt ion), between about 10-40 g(H₃BO₃)/l (e.g., boric acid), and about 0.01-0.1 g (H₂SO₄)/L (e.g.,sulfuric acid). In a specific example, the secondary electroplatingsolution contains about 0 g/l of cobalt ion, about 30 g/l boric acid,and about 0.1 g/l sulfuric acid. The plating electrolyte concentrationcould be maintained by dosing secondary electrolyte when [Me+] incathodic side drift high; this will bring [Me+] down to target withoutimpacting other components; dosing acid when [H⁺] in the cathodicportion drift low.

The secondary electrolyte could also be designed to have significantlyhigher H₃BO₃ concentration than in the primary electrolyte. For example,the secondary electroplating solution may have between 0-1 g/l cobaltion, between about 40-50 g/l boric acid, and about 0.01-0.1 g/l sulfuricacid. In a specific example, the secondary electroplating solution hasabout 3 g/l Co²⁺, about 45 g/l boric acid, and about 0.1 g/l sulfuricacid. The plating electrolyte concentration could be maintained bydosing DI to the central bath when Co²⁺ drift high; this will bring[Me⁺] down to target while at the same time, diluting acid and H₃BO₃concentration; the acid concentration could be compensated with aciddosing, while the H₃BO₃ concentration could be brought up by dosing thesecondary electrolyte.

The above two approaches could be combined by adopting a secondaryelectrolyte with significantly lower Co²⁺ concentration andsignificantly higher H₃BO₃ concentration. For example, the secondaryelectroplating solution may have between 0-1 g/l cobalt ion, betweenabout 40-50 g/L boric acid, and about 0.01-0.1 g/l sulfuric acid. In aspecific example, the secondary electroplating solution has about 0 g/lcobalt ion, about 45 g/l boric acid, and about 0.1 g/l sulfuric acid.

FIGS. 10A-10C illustrate how the three major components respond overtime with secondary electrolyte dosing implemented on the platingapparatus with lower metal ion concentration secondary electrolyteapproach as described.

Example 3— Electroplating in Systems Having an Auxiliary Electrode

Certain configurations of electroplating systems and/or apparatuses mayinclude an auxiliary electrode chamber contained therein, or connectedthereto. Such an auxiliary electrode chamber may be controlled locally,or centrally.

As described in previous sections, it is common for a plating apparatusto have more than one cathode or anode chamber. At times, theconcentration of the electrolyte component in the auxiliary electrodechamber needs to be different from the main cathodic solution. One suchexample is illustrated in FIG. 11A. In this apparatus, there is asecondary cathode that is contained in a separate chamber. The secondarycathode is added to help maintain the performance of the main cathode(wafer substrate) (to improve plating uniformity on wafer, for example).To support higher plating current capability on the dual cathode, it isdesirable to have higher anion concentration in the electrolyte than inthe main cathodic solution, yet the usage of the secondary electrolyteis not significant. Adding a secondary electrolyte source through abottle (or through facility supply) with significantly high anionconcentration would help significantly increase the dual cathode currentcapability since the current the electrolyte could support without gasevolution is directly proportional to the concentration of the anion inthe electrolyte. The actual electrolyte to be used in the secondarycathodic chamber could be secondary electrolyte itself, or could be amixture of secondary electrolyte with the primary electrolyte, dependingon the needs of secondary cathode plating current.

In one example, the primary electroplating solution contains about 1-5g/l copper ion, while the secondary electroplating solution, which isprovided to one or more auxiliary cathodes contains about 30-70 g/lcopper ion. This may increase DC current capability in the auxiliarycathodes by about 6-70 times.

System 1100A, shown by FIG. 11A, likewise builds upon that introduced bysystem 100 shown by FIG. 1 earlier. Like reference numerals refer tolike elements, thus a redundant description of the same will be omitted.Secondary plating electrolyte is delivered, or flowed, via line 1102into the cathodic side 122. In certain embodiments, solution containedin the auxiliary cathode may be the secondary plating electrolyte alone,or a mixture of the secondary plating electrolyte and the incomingplating electrolyte depending on the particular needs of a givenapplication. FIG. 11B shows graph 1100B of the maximum auxiliary currentas a function of cation concentration in the solution. Graph 1100Bincludes data generated with secondary electrolyte dosing of variousconcentration levels, e.g., shown by area 1102B, as well as a baselinedata value without secondary electrolyte, e.g. show by area 1104B.

Example (4)—Cobalt Electroplating with Secondary Electrolyte to CathodeChamber

The cathode electrolyte concentration on a plating apparatus may becontrolled by adopting secondary electrolyte on the anode side, e.g.,flowing secondary electrolyte directly into the anode chamber. Asprevious described, one potential problem with the mass/charge balancein a Co-like plating system is that more metal ion is released from theanode to the plating electrolyte than pulled out of the electrolyte byplating onto the cathode; while hydrogen ions are consumed without beingreplenished on the cathode side. Thus over time, metal ion concentrationdrift up, and acid concentration drift down.

By introducing into the anode chamber a secondary electrolyte withhigher acid, and low or zero metal ion concentration, the system mayutilize the selectivity of the cation exchange membrane in transferringhydrogen ions and metal ions to let more hydrogen ion passing themembrane to replenish acid (which was consumed during plating process),and let less metal ion pass through the membrane to avoid accumulation.In this way, provision of the secondary electrolyte to the anode chamberhelps to balance the metal ion and hydrogen ion consumption andgeneration/adding rate in the cathode side.

In some embodiments, the primary electroplating solution contains about2-40 g/L cobalt ion, about 10-40 g/l boric acid, about 0.01-0.1 g/lsulfuric acid, and about 20-400 ppm additives (e.g., about 3 g/l cobaltion, about 0.1 g/l sulfuric acid, and about 30 g/l boric acid). In suchembodiments, the secondary electroplating solution may contain about 0-1g/l cobalt ion, about 0.1-0.5 g/l sulfuric acid, and about 0-40 g/lboric acid (e.g., about 0 g/l cobalt ion, about 2 g/l sulfuric acid, andabout 30 g/l boric acid).

As may result from operating a system 1200 shown in FIG. 12, theconcentrations of all components contained within the primaryelectroplating solution and the cathode chamber may be stable overlong-term. Likewise, the anode side solution concentrations may alsostabilize over time to a level that is different from the targetconcentrations, due to the addition of secondary electrolyte with asignificantly higher acid content.

FIGS. 13A-13C illustrate generally stable concentrations of cobalt ion,sulfuric acid, and boric acid in the primary electroplating solution ofa cobalt plating system employing direct anode chamber injection of asecondary electroplating solution as illustrated in FIG. 12. FIGS. 13Dand 13E illustrate generally stable concentrations of cobalt ion andsulfuric acid in the anolyte of the cobalt plating system employingdirect anode chamber injection of a secondary electroplating solution asillustrated in FIG. 12. Note that “SAC” in the figures refers to theanode chamber (separated anode chamber).

While similar to the other systems discussed earlier, system 1200 variesfrom system 100 in flowing secondary electrolyte directly to the anodechamber 126 to assist with stabilizing electroplating solutioncompositions. Note that systems employing direct anode chamberintroduction of secondary electroplating solution are not limited tocobalt plating; they can in some cases be used for plating other metals.

Apparatus

Many apparatus configurations may be used in accordance with theembodiments described herein. One example apparatus includes a clamshellfixture that seals a wafer's backside away from the plating solutionwhile allowing plating to proceed on the wafer's face. The clamshellfixture may support the wafer, for example, via a seal placed over thebevel of the wafer, or by means such as a vacuum applied to the back ofa wafer in conjunction with seals applied near the bevel.

The clamshell fixture should enter the bath in a way that allows goodwetting of the wafer's plating surface. The quality of substrate wettingis affected by multiple variables including, but not limited to,clamshell rotation speed, vertical entry speed, and the angle of theclamshell relative to the surface of the plating bath. These variablesand their effects are further discussed in U.S. Pat. No. 6,551,487,incorporated by reference herein. In certain implementations, theelectrode rotation rate is between about 5-125 RPM, the vertical entryspeed is between about 5-300 mm/s, and the angle of the clamshellrelative to the surface of the plating bath is between about 1-10degrees. One of the goals in optimizing these variables for a particularapplication is to achieve good wetting by fully displacing air from thewafer surface.

The electrodeposition methods disclosed herein can be described inreference to, and may be employed in the context of, variouselectroplating tool apparatuses. One example of a plating apparatus thatmay be used according to the embodiments herein is the Lam ResearchSabre tool. Electrodeposition, including substrate immersion, and othermethods disclosed herein can be performed in components that form alarger electrodeposition apparatus. FIG. 14 shows a schematic of a topview of an example electrodeposition apparatus. The electrodepositionapparatus 1400 can include three separate electroplating modules 1402,1404, and 1406. The electrodeposition apparatus 1400 can also includethree separate modules 1412, 1414, and 1416 configured for variousprocess operations. For example, in some embodiments, one or more ofmodules 1412, 1414, and 1416 may be a spin rinse drying (SRD) module. Inother embodiments, one or more of the modules 1412, 1414, and 1416 maybe post-electrofill modules (PEMs), each configured to perform afunction, such as edge bevel removal, backside etching, and acidcleaning of substrates after they have been processed by one of theelectroplating modules 1402, 1404, and 1406.

The electrodeposition apparatus 1400 includes a centralelectrodeposition chamber 1424. The central electrodeposition chamber1424 is a chamber that holds the chemical solution used as theelectroplating solution in the electroplating modules 1402, 1404, and1406. The electrodeposition apparatus 1400 also includes a dosing system1426 that may store and deliver additives for the electroplatingsolution. A chemical dilution module 1422 may store and mix chemicals tobe used as an etchant. A filtration and pumping unit 1428 may filter theelectroplating solution for the central electrodeposition chamber 1424and pump it to the electroplating modules.

A system controller 1430 provides electronic and interface controlsrequired to operate the electrodeposition apparatus 1400. The systemcontroller 1430 (which may include one or more physical or logicalcontrollers) controls some or all of the properties of theelectroplating apparatus 1400. The system controller 1430 typicallyincludes one or more memory devices and one or more processors. Theprocessor may include a central processing unit (CPU) or computer,analog and/or digital input/output connections, stepper motor controllerboards, and other like components. Instructions for implementingappropriate control operations as described herein may be executed onthe processor. These instructions may be stored on the memory devicesassociated with the system controller 1430 or they may be provided overa network. In certain embodiments, the system controller 1430 executessystem control software.

The system logic (e.g., control software) in the electrodepositionapparatus 1400 may include instructions for controlling the timing,mixture of electrolyte components (including the concentration of one ormore electrolyte components), inlet pressure, plating cell pressure,plating cell temperature, substrate temperature, current and potentialapplied to the substrate and any other electrodes, substrate position,substrate rotation, and other parameters of a particular processperformed by the electrodeposition apparatus 1400. The system controllogic may also include instructions for electroplating under conditionsthat are tailored to be appropriate for a low copper concentrationelectrolyte. For example, the system control logic may be configured toprovide a relatively low current density during the bottom-up fill stageand/or a higher current density during the overburden stage. The controllogic may also be configured to provide certain levels of mass transferto the wafer surface during plating. For example, the control logic maybe configured to control the flow of electrolyte to ensure sufficientmass transfer to the wafer during plating such that the substrate doesnot encounter depleted copper conditions. In certain embodiments thecontrol logic may operate to provide different levels of mass transferat different stages of the plating process (e.g., higher mass transferduring the bottom-up fill stage than during the overburden stage, orlower mass transfer during the bottom-up fill stage than during theoverburden stage). Further, the system control logic may be configuredto maintain the concentration of one or more electrolyte componentswithin any of the ranges disclosed herein. As a particular example, thesystem control logic may be designed or configured to maintain theconcentration of copper cations between about 1-10 g/l. System controllogic may be configured in any suitable way. For example, variousprocess tool component sub-routines or control objects may be written tocontrol operation of the process tool components used to carry outvarious process tool processes. System control software may be coded inany suitable computer readable programming language. The logic may alsobe implemented as hardware in a programmable logic device (e.g., anFPGA), an ASIC, or other appropriate vehicle.

In some embodiments, system control logic includes input/output control(IOC) sequencing instructions for controlling the various parametersdescribed above. For example, each phase of an electroplating processmay include one or more instructions for execution by the systemcontroller 1430. The instructions for setting process conditions for animmersion process phase may be included in a corresponding immersionrecipe phase. In some embodiments, the electroplating recipe phases maybe sequentially arranged, so that all instructions for an electroplatingprocess phase are executed concurrently with that process phase.

The control logic may be divided into various components such asprograms or sections of programs in some embodiments. Examples of logiccomponents for this purpose include a substrate positioning component,an electrolyte composition control component, a pressure controlcomponent, a heater control component, and a potential/current powersupply control component.

In some embodiments, there may be a user interface associated with thesystem controller 1430. The user interface may include a display screen,graphical software displays of the apparatus and/or process conditions,and user input devices such as pointing devices, keyboards, touchscreens, microphones, etc.

In some embodiments, parameters adjusted by the system controller 1430may relate to process conditions. Non-limiting examples include bathconditions (temperature, composition, and flow rate), substrate position(rotation rate, linear (vertical) speed, angle from horizontal) atvarious stages, etc. These parameters may be provided to the user in theform of a recipe, which may be entered utilizing the user interface.

Signals for monitoring the process may be provided by analog and/ordigital input connections of the system controller 1430 from variousprocess tool sensors. The signals for controlling the process may beoutput on the analog and digital output connections of the process tool.Non-limiting examples of process tool sensors that may be monitoredinclude mass flow controllers, pressure sensors (such as manometers),thermocouples, optical position sensors, etc. Appropriately programmedfeedback and control algorithms may be used with data from these sensorsto maintain process conditions.

In one embodiment, the instructions can include inserting the substratein a wafer holder, tilting the substrate, biasing the substrate duringimmersion, and electrodepositing a copper containing structure on asubstrate.

A hand-off tool 1440 may select a substrate from a substrate cassettesuch as the cassette 1442 or the cassette 1444. The cassettes 1442 or1444 may be front opening unified pods (FOUPs). A FOUP is an enclosuredesigned to hold substrates securely and safely in a controlledenvironment and to allow the substrates to be removed for processing ormeasurement by tools equipped with appropriate load ports and robotichandling systems. The hand-off tool 1440 may hold the substrate using avacuum attachment or some other attaching mechanism.

The hand-off tool 1440 may interface with a wafer handling station 1432,the cassettes 1442 or 1444, a transfer station 1450, or an aligner 1448.From the transfer station 1450, a hand-off tool 1446 may gain access tothe substrate. The transfer station 1450 may be a slot or a positionfrom and to which hand-off tools 1440 and 1446 may pass substrateswithout going through the aligner 1448. In some embodiments, however, toensure that a substrate is properly aligned on the hand-off tool 1446for precision delivery to an electroplating module, the hand-off tool1446 may align the substrate with an aligner 1448. The hand-off tool1446 may also deliver a substrate to one of the electroplating modules1402, 1404, or 1406 or to one of the three separate modules 1412, 1414,and 1416 configured for various process operations.

An example of a process operation according to the methods describedabove may proceed as follows: (1) electrodeposit copper onto a substrateto form a copper containing structure in the electroplating module 1404;(2) rinse and dry the substrate in SRD in module 1412; and, (3) performedge bevel removal in module 1414.

An apparatus configured to allow efficient cycling of substrates throughsequential plating, rinsing, drying, and PEM process operations may beuseful for implementations for use in a manufacturing environment. Toaccomplish this, the module 1412 can be configured as a spin rinse dryerand an edge bevel removal chamber. With such a module 1412, thesubstrate would only need to be transported between the electroplatingmodule 1404 and the module 1412 for the copper plating and EBRoperations.

In some implementations, a controller (e.g., system controller 1430) ispart of a system, which may be part of the above-described examples. Thecontroller may contain control logic or software and/or executeinstructions provided from another source. Such systems can includesemiconductor processing equipment, including a processing tool ortools, chamber or chambers, a platform or platforms for processing,and/or specific processing components (a wafer pedestal, a gas flowsystem, etc.). These systems may be integrated with electronics forcontrolling their operation before, during, and after processing of asemiconductor wafer or substrate. The electronics may be referred to asthe “controller,” which may control various components or subparts ofthe system or systems. The controller, depending on the processingrequirements and/or the type of system, may be programmed to control anyof the processes disclosed herein, including the delivery of processinggases, temperature settings (e.g., heating and/or cooling), pressuresettings, vacuum settings, power settings, radio frequency (RF)generator settings, RF matching circuit settings, frequency settings,flow rate settings, fluid delivery settings, positional and operationsettings, wafer transfers into and out of a tool and other transfertools and/or load locks connected to or interfaced with a specificsystem.

Broadly speaking, the controller may be defined as electronics havingvarious integrated circuits, logic, memory, and/or software that receiveinstructions, issue instructions, control operations described herein,enable cleaning operations, enable endpoint measurements, metrology, andthe like. The integrated circuits may include chips in the form offirmware that store program instructions, digital signal processors(DSPs), chips defined as application specific integrated circuits(ASICs), and/or one or more microprocessors, or microcontrollers thatexecute program instructions (e.g., software). Program instructions maybe instructions communicated to the controller in the form of variousindividual settings (or program files), defining operational parametersfor carrying out a particular process on or for a semiconductor wafer orto a system. The operational parameters may, in some embodiments, bepart of a recipe defined by process engineers to accomplish one or moreprocessing steps during the fabrication of one or more layers,materials, metals, oxides, silicon, silicon dioxide, surfaces, circuits,and/or dies of a wafer.

The controller, in some implementations, may be a part of or coupled toa computer that is integrated with, coupled to the system, otherwisenetworked to the system, or a combination thereof. For example, thecontroller may be in the “cloud” or all or a part of a fab host computersystem, which can allow for remote access of the wafer processing. Thecomputer may enable remote access to the system to monitor currentprogress of fabrication operations, examine a history of pastfabrication operations, examine trends or performance metrics from aplurality of fabrication operations, to change parameters of currentprocessing, to set processing steps to follow a current processing, orto start a new process. In some examples, a remote computer (e.g. aserver) can provide process recipes to a system over a network, whichmay include a local network or the Internet. The remote computer mayinclude a user interface that enables entry or programming of parametersand/or settings, which are then communicated to the system from theremote computer. In some examples, the controller receives instructionsin the form of data, which specify parameters for each of the processingsteps to be performed during one or more operations. It should beunderstood that the parameters may be specific to the type of process tobe performed and the type of tool that the controller is configured tointerface with or control. Thus as described above, the controller maybe distributed, such as by comprising one or more discrete controllersthat are networked together and working towards a common purpose, suchas the processes and controls described herein. An example of adistributed controller for such purposes would be one or more integratedcircuits on a chamber in communication with one or more integratedcircuits located remotely (such as at the platform level or as part of aremote computer) that combine to control a process on the chamber.

Without limitation, example systems may include a plasma etch chamber ormodule, a deposition chamber or module, a spin-rinse chamber or module,a metal plating chamber or module, a clean chamber or module, a beveledge etch chamber or module, a physical vapor deposition (PVD) chamberor module, a chemical vapor deposition (CVD) chamber or module, anatomic layer deposition (ALD) chamber or module, an atomic layer etch(ALE) chamber or module, an ion implantation chamber or module, a trackchamber or module, and any other semiconductor processing systems thatmay be associated or used in the fabrication and/or manufacturing ofsemiconductor wafers.

As noted above, depending on the process step or steps to be performedby the tool, the controller might communicate with one or more of othertool circuits or modules, other tool components, cluster tools, othertool interfaces, adjacent tools, neighboring tools, tools locatedthroughout a factory, a main computer, another controller, or tools usedin material transport that bring containers of wafers to and from toollocations and/or load ports in a semiconductor manufacturing factory.

An alternative embodiment of an electrodeposition apparatus 1500 isschematically illustrated in FIG. 15. In this embodiment, theelectrodeposition apparatus 1500 has a set of electroplating cells 1507,each containing an electroplating bath, in a paired or multiple “duet”configuration. In addition to electroplating per se, theelectrodeposition apparatus 1500 may perform a variety of otherelectroplating related processes and sub-steps, such as spin-rinsing,spin-drying, metal and silicon wet etching, electroless deposition,pre-wetting and pre-chemical treating, reducing, annealing, photoresiststripping, and surface pre-activation, for example. Theelectrodeposition apparatus 1500 is shown schematically looking top downin FIG. 15, and only a single level or “floor” is revealed in thefigure, but it is to be readily understood by one having ordinary skillin the art that such an apparatus, e.g. the Lam Sabre™ 3D tool, can havetwo or more levels “stacked” on top of each other, each potentiallyhaving identical or different types of processing stations.

Referring once again to FIG. 15, the substrates 1506 that are to beelectroplated are generally fed to the electrodeposition apparatus 1500through a front end loading FOUP 1501 and, in this example, are broughtfrom the FOUP to the main substrate processing area of theelectrodeposition apparatus 1500 via a front-end robot 1502 that canretract and move a substrate 1506 driven by a spindle 1503 in multipledimensions from one station to another of the accessible stations—twofront-end accessible stations 1504 and also two front-end accessiblestations 1508 are shown in this example. The front-end accessiblestations 1504 and 1508 may include, for example, pre-treatment stations,and spin rinse drying (SRD) stations. Lateral movement from side-to-sideof the front-end robot 1502 is accomplished utilizing robot track 1502a. Each of the substrates 1506 may be held by a cup/cone assembly (notshown) driven by a spindle 1503 connected to a motor (not shown), andthe motor may be attached to a mounting bracket 1509. Also shown in thisexample are the four “duets” of electroplating cells 1507, for a totalof eight electroplating cells 1507. The electroplating cells 1507 may beused for electroplating copper for the copper containing structure andelectroplating solder material for the solder structure. A systemcontroller (not shown) may be coupled to the electrodeposition apparatus1500 to control some or all of the properties of the electrodepositionapparatus 1500. The system controller may be programmed or otherwiseconfigured to execute instructions according to processes describedearlier herein.

The electroplating apparatus/methods described hereinabove may be usedin conjunction with lithographic patterning tools or processes, forexample, for the fabrication or manufacture of semiconductor devices,displays, LEDs, photovoltaic panels and the like. Generally, though notnecessarily, such tools/processes will be used or conducted together ina common fabrication facility. Lithographic patterning of a filmgenerally includes some or all of the following steps, each step enabledwith a number of possible tools: (1) application of photoresist on awork piece, i.e., a substrate, using a spin-on or spray-on tool; (2)curing of photoresist using a hot plate or furnace or UV curing tool;(3) exposing the photoresist to visible, UV, or x-ray light with a toolsuch as a wafer stepper; (4) developing the resist so as to selectivelyremove resist and thereby pattern it using a tool such as a wet bench;(5) transferring the resist pattern into an underlying film or workpiece by using a dry or plasma-assisted etching tool; and (6) removingthe resist using a tool such as an RF or microwave plasma resiststripper.

It is to be understood that the configurations and/or approachesdescribed herein are exemplary in nature, and that these specificembodiments or examples are not to be considered in a limiting sense,because numerous variations are possible. The specific routines ormethods described herein may represent one or more of any number ofprocessing strategies. As such, various acts illustrated may beperformed in the sequence illustrated, in other sequences, in parallel,or in some cases omitted. Likewise, the order of the above describedprocesses may be changed.

The subject matter of the present disclosure includes all novel andnonobvious combinations and sub-combinations of the various processes,systems and configurations, and other features, functions, acts, and/orproperties disclosed herein, as well as any and all equivalents thereof.

What is claimed is:
 1. A method of electroplating a metal onto asubstrate during fabrication of a device, the method comprising: (a)providing an electroplating solution to an electroplating systemcomprising: (i) an electroplating cell comprising an anode chamber and acathode chamber and configured to hold the substrate in the cathodechamber while electroplating the metal onto the substrate, (ii) anelectroplating solution reservoir configured to hold a portion of theelectroplating solution while electroplating the metal onto thesubstrate, (iii) a recirculation system for delivering theelectroplating solution between the electroplating cell and theelectroplating solution reservoir, (iv) a make-up solution inlet forproviding make-up solution to the electroplating system, and (v) asecondary electroplating solution inlet for providing a secondaryelectroplating solution to the electroplating system, wherein theelectroplating solution comprises multiple components for electroplatingthe metal onto the substrate; (b) electroplating the metal onto thesubstrate while the substrate is held in the cathode chamber; (c)supplying the make-up solution to the electroplating system via themake-up solution inlet, wherein the make-up solution comprises some orall of the multiple components, each at a target concentration forelectroplating the metal onto the substrate, wherein supplying themake-up solution to the electroplating system changes a composition ofthe electroplating solution so that at least one of the multiplecomponents in the electroplating solution moves closer to its targetconcentration; and (d) supplying the secondary electroplating solutionto the electroplating system via the secondary electroplating solutioninlet, wherein the secondary electroplating solution comprises some orall of the multiple components, and wherein at least one of thefollowing conditions is satisfied: (1) the secondary electroplatingsolution comprises at least one of the multiple components at asecondary concentration that is significantly higher than its targetconcentration and an additional component of the multiple components ata secondary concentration that is either substantially the same as itstarget concentration or significantly lower than its targetconcentration, and/or (2) the secondary electroplating solutioncomprises at least one of the multiple components at a secondaryconcentration that is significantly lower than its target concentration,and an additional component of the multiple components at a secondaryconcentration that is substantially the same as its targetconcentration.